The present invention relates to a data transmission system, a method and apparatus for processing information, a method and apparatus for relaying data, a storage medium, and a program. More particularly, the present invention relates to a data transmission system, a method and apparatus for processing information, a method and apparatus for relaying data, a storage medium, and a program, in which a mediator unit is disposed in a communication path different from a communication path of data transmission so that, in data transmission, the mediator unit authenticates a user of a device at a transmitting end and checks the ability or the state of a device at a receiving end, thereby ensuring that even large-size data can be transmitted and received in a highly reliable fashion.
In recent years, networks such as the Internet have become very popular. As a result, it has become popular to transmit or receive electronic mails or files via the networks. Furthermore, broad band networks have become available, and it has become possible to transmit or receive large-size data such as image data or music data.
When a sender transmits an electronic mail, the sender generally transmits it together with data indicating information associated with the sender such as a sender name to a known address of a receiving terminal apparatus, without caring about the situation or the status of the receiving terminal apparatus.
In the case in which data is transferred using the FTP (File Transfer Protocol), a called information processing apparatus (host computer) authenticates a user of a calling terminal (client). For example, when data is downloaded using the FTP, if a client accesses a host computer, the host computer authenticates a user of the client. If the authentication has been successfully passed, the client retrieves desired data from the host computer and downloads the data. When data is uploaded, the host computer performs user authentication in a similar manner. That is, if the user authentication is successfully passed, the client accesses a desired directory of the host computer and uploads data thereinto.
Furthermore, in recent years, file exchange service has become available. In the file exchange service, a file is exchanged directly between client PCs via the Internet using dedicated software.
For example, if a user installs such client software onto his/her terminal device and executes the client software, the terminal device is automatically connected to a file exchange service information server on the Internet, and a list of data stored by the terminal device and allowed to be brought on public view is transmitted to the server. A user of the terminal device connected to the file exchange service information server can retrieve desired data on the basis of information associated with the data, such as a file name. If the user issues a download command by operating his/her terminal device, the file exchange service information server supplies information associated with a client at which the data is stored. In accordance with the supplied information, the user can download the data directly from the client at which the data is stored.
However, when electronic mails are transmitted in the above-described manner, a receiver receives an electronic mail transmitted from a sender who is not authenticated, and thus the receiver cannot say whether the mail is from a real or bogus sender.
In the case in which data is transferred using the FTP, user authentication is performed by a device from which data is to be transferred. However, it is difficult that each host computer on the Internet performs user authentication on a great number of clients. In many cases, because of the above difficulty, users can freely access a host computer using an account such as anonymous account put on public view. That is, an unidentified user can access a host computer. This results in low security in data transmission.
One technique to avoid the above problem is to dispose a distribution server between a receiving information processing apparatus and a transmitting information processing apparatus and authenticate a user of the receiving information processing apparatus using the distribution server. However, in this technique, when large-size data such as motion image data, still image data, or music data is transferred, large load is imposed on the distribution server disposed at an intermediate location and the total system performance is degraded.
Another possible technique is to use the conventional file exchange system and perform user authentication using a central server. However, the central server performs only user authentication, and transmission of data is performed directly among clients.
In this technique, however, when large-size data is transmitted, a terminal device at a transmitting end transmits the data without caring about the ability or the current status of a terminal device at a receiving end. Thus, if the receiving ability of the terminal device at the receiving end is low as is the case with a low available storage space, the terminal device at the receiving end cannot receive data or a reduction in processing speed occurs. A problem also occurs at the transmitting end. That is, if the terminal device at the transmitting end starts transmission of data when the terminal device at the receiving end is in a state in which the data cannot be received, a reduction in the processing speed of the terminal device at the transmitting end occurs.